1. Field of the Invention
This invention relates to a compression ring for internal-combustion engines.
2. Description of the Prior Art
With regard to compression rings, which represent one type of piston ring for internal-combustion engines, various improvements in compression-ring sealability have been made for the purpose of preventing leakage of gas when a piston is acted upon by pressure.
An example of such a compression ring, the construction of which is shown in FIG. 9, is one having special butt ends. In this example, a compression ring 1 has two butt end faces one of which is formed to have a rib 2 projecting circumferentially from an upper outer circumferential side thereof. The rib 2 has a cross section in the shape of a right-angled triangle. The other butt end face of the compression ring 1 is formed to have a notch 3 in an upper outer circumferential side thereof. The notch 3 also has a cross section in the shape of a right-angled triangle and is capable of receiving the rib 2. The compression ring 1 is fitted snugly into the ring groove of a piston, in which state the two butt portions of the ring meet each other.
In order to improve the seal at the side face of the compression ring, the upper corner portion on the inner circumferential side of the compression ring is cut away along the entire circumference of the ring to form an inner cut. If the inner-cut portion, shown at numeral 4, extends to the slanting surfaces of the opposing butt end faces of the compression ring 1, as illustrated in FIG. 10, the gas or oil to be sealed in travels along the back surface of the ring 1 and escapes from the inner cut 4 through the gap between the rib 2 and the notch 3. The result is the same as that seen in a compression ring having the well-known stepped butt end faces, shown in FIG. 11, in which the two end faces of the ring are provided with steps 5 that engage each other. In FIG. 11, the arrow indicates the path along which a gas bleeds and escapes to the outside. Accordingly, it is required that the cross-sectional dimensions of the rib 2 be reduced in conformity with the size of the inner cut. However, a consequence of reducing the cross-sectional dimensions of the rib 2 can be a failure to obtain the requisite mechanical strength.